The invention relates to an image pickup apparatus and a signal processing method which are suitable for use in a video camera for recording a video signal based on an image pickup signal photographed by an image pickup device onto a recording medium such as magnetic tape, optical disc, or the like and, more particularly, to an automatic focusing control.
A video camera for recording a video signal based on an image pickup-signal from a CCD (Charge Coupled Device) image pickup device onto a magnetic tape has been widespread. Recently, a digital video camera for recording a digital video signal based on an image pickup signal from the CCD image pickup device onto a magnetic disk, an optical disk, a semiconductor memory, or the like has been put into practical use. An automatic focusing function for controlling a focusing lens to an in-focus point is provided for such a video camera.
FIG. 1 shows a construction of a main portion regarding the automatic focusing function of a conventional video camera. The automatic focusing function uses what is called a contrast detecting method for performing a focusing control by using the principle in which a high frequency component of a luminance signal becomes maximum at the in-focus point.
In FIG. 1, reference numeral 101 denotes a lens portion. The lens portion 101 has: a lens group comprising a zoom lens, a focusing lens, and the like; an aperture mechanism; its driving circuit; and the like. An image pickup unit is constructed by the lens portion 101 and a CCD image pickup device 102. A position of the focusing lens in the lens portion 101 is controlled by control information from a microcomputer 110.
Object image light derived via the lens portion 101 is formed as an image onto the image pickup surface of the CCD image pickup device 102 and the object image light is photoelectrically converted. An output of the CCD image pickup device 102 is supplied to a sample/hold and AGC (Automatic Gain Control) circuit 103. An output of the CCD image pickup device 102 is sampled and held and amplified to a proper level by the sample/hold and AGC circuit 103.
An output of the sample/hold and AGC circuit 103 is supplied to an A/D converting circuit 104. In the A/D converting circuit 104, the image pickup signal is digitized. An output of the A/D converting circuit 104 is supplied to each of a chroma signal separating circuit 105 and a luminance signal separating circuit 106 of a camera signal processing circuit 114. In the chroma signal separating circuit 105, a chroma signal is separated and this chroma signal is taken out from an output terminal 111. In the luminance signal separating circuit 106, a luminance signal is separated and this luminance signal is taken out from an output terminal 112.
An automatic focus detecting circuit 115 is constructed by a high pass filter 113, a gate circuit 107, a range finder frame generating circuit 108, and an integrating circuit 109. The luminance signal separated by the luminance signal separating circuit 106 is supplied to the high pass filter 113. A high frequency component in the luminance signal is extracted by the high pass filter 113. A high frequency component level of the luminance signal is detected. An output of the high pass filter 113 is supplied to the gate circuit 107. A window signal for setting a range finder frame is supplied to the gate circuit 107 from the range finder frame generating circuit 108. A detection output at a predetermined timing corresponding to the range finder frame is taken out by the gate circuit 107. An output of the gate circuit 107 is supplied to the integrating circuit 109. In the integrating circuit 109, the high frequency component level of the luminance signal is integrated and an evaluation value is obtained. This evaluation value is supplied to the microcomputer 110.
The microcomputer 110 fetches the evaluation value while moving the focusing lens of the lens portion 101 and controls the focusing lens to the in-focus position on the basis of the evaluation value. That is, the high frequency component level of the luminance signal becomes maximum at the in-focus position. Therefore, while wobbling the focusing lens back and forth at a predetermined low frequency by the microcomputer 110, a point where the evaluation value becomes maximum is searched. This point where the evaluation value becomes maximum is set to the in-focus point of the focusing lens.
As mentioned above, in the conventional video camera, the automatic focus detecting circuit 115 is constructed by the high pass filter 113, gate circuit 107, range finder frame generating circuit 108, and integrating circuit 109. The evaluation value obtained from the automatic focus detecting circuit 115 is supplied to the microcomputer 110. The position of the focusing lens is controlled by the microcomputer 110 on the basis of the evaluation value. The automatic focus detecting circuit 115 of such a conventional video camera has such a problem that a circuit scale is large because the high pass filter 113 and integrating circuit 109 exist.
Particularly, in the conventional video camera, the camera signal processing circuit 114 and automatic focus detecting circuit 115 are arranged on separate circuit boards. In such a separate construction, however, the circuit scale enlarges and an electric power consumption increases. It is, therefore, considered to arrange the camera signal processing circuit 114 and automatic focus detecting circuit 115 onto a same circuit board. In case of such an integrated structure, it is demanded to reduce the circuit scale in order to further decrease the gate scale.
It is, therefore, an object of the invention to provide an image pickup apparatus and a signal processing method which can solve the above problems.
To solve the above problems, according to the invention, there is provided an image pickup apparatus comprising: a luminance signal extracting unit for extracting a luminance signal from an image pickup signal photographed by a solid state image pickup device; a filter for extracting at least a high frequency component in the luminance signal extracted by the luminance signal extracting unit; a gain control unit for varying a gain of at least the high frequency component in the luminance signal extracted by the filter; an outline emphasizing unit for emphasizing an edge portion by adding the luminance signal from the luminance signal extracting unit and at least the high frequency component in the luminance signal in which the gain has been varied by the gain control unit; and a control unit for controlling an in-focus point by driving a focusing lens on the basis of a level of at least the high frequency component in the luminance signal extracted by the filter, wherein the image pickup signal photographed by the solid state image pickup device is processed.